The present invention relates to a boron-phosphide-based semiconductor device having a hetero junction structure; and particularly to a boron-phosphide-based semiconductor light-emitting device exhibiting high emission intensity and method for producing the same.
Boron phosphide (BP) has been traditionally known as a Group III-V compound semiconductor (see Nature, 179, No. 4569 (1957), p. 1075). Since boron phosphide (BP) is an indirect-transition-type semiconductor (see xe2x80x9cAn Introduction to Semiconductor Devicexe2x80x9d authored by Iwao Teramoto, first edition, published by Baifukan Co., Ltd. on Mar. 30, 1995, p. 28), BP is considered to be unsuitable for use as a material for formation of a light-emitting layer of a semiconductor light-emitting device. In a conventional boron-phosphide-based semiconductor light-emitting diode (LED) incorporating a boron-phosphide-based semiconductor layer, the boron-phosphide-based semiconductor layer formed of, for example, boron phosphide serves therefore as a buffer layer provided on a single-crystal silicon substrate (see U.S. Pat. No. 6,069,021). Meanwhile, in a laser diode (LD), a boron-phosphide-based semiconductor layer serves as, for example, a contact layer for formation of an ohmic electrode (see Japanese Patent Application Laid-Open (kokai) No. 2-288388).
In general, a light-emitting layer of a semiconductor light-emitting device is formed of a direct-transition-type semiconductor material, which exhibits higher radiative recombination efficiency as compared with an indirect-transition-type semiconductor. In many cases, a light-emitting layer of a boron-phosphide-based semiconductor LED has been conventionally formed of gallium indium nitride (GaXIn1xe2x88x92XN:0xe2x89xa6Xxe2x89xa61) (see Japanese Patent Publication (kokoku) No. 55-3834). A light-emitting layer has been formed especially from GaXIn1xe2x88x92XN(0xe2x89xa6Xxe2x89xa61) which is intentionally doped with an element belonging to Group IV of the periodic table, such as silicon (Si) or germanium (Ge) (see Japanese Patent Application Laid-Open (kokai) No. 6-260680). This is because doping with a Group IV element has been disclosed as producing a GaXIn1xe2x88x92XN(0xe2x89xa6Xxe2x89xa61) light-emitting layer of high emission intensity (see Japanese Patent No. 2560963). In order to produce a semiconductor light-emitting device exhibiting high emission intensity, a light-emitting portion thereof is generally formed of a pn-junction-type double hetero (DH) structure including a light-emitting layer, and p-type and n-type cladding layers which sandwich the light-emitting layer (see Japanese Patent Application Laid-Open (kokai) No. 6-260283).
Conventionally, a p-type boron-phosphide-based semiconductor layer has generally been formed through intentional doping with an element belonging to Group II of the periodic table, such as magnesium (Mg) or zinc (Zn) (see (1) Japanese Patent Application Laid-Open (kokai) No. 2-275682, (2) Japanese Patent Application Laid-Open (kokai) No. 2-288371, (3) Japanese Patent Application Laid-Open (kokai) No. 2-288388, (4) Japanese Patent Application Laid-Open (kokai) No. 10-242514, (5) Japanese Patent Application Laid-Open (kokai) No. 10-242515, and (6) Japanese Patent Application Laid-Open (kokai) No. 10-242567). Meanwhile, an n-type boron-phosphide-based semiconductor layer has generally been formed through doping with a Group IV element such as silicon (Si) (see, for example, Japanese Patent Application Laid-Open (kokai) No. 2-288388). In view of the foregoing, a p-type cladding layer constituting a light-emitting portion of pn-junction-type DH structure has been formed of a p-type boron-phosphide-based semiconductor layer doped with, for example, Mg or Zn. Meanwhile, an n-type cladding layer has been formed of an n-type boron-phosphide-based semiconductor layer doped with silicon (see Japanese Patent Application No. 2001-158282).
Silicon (Si), which is a Group IV element, is described as serving as an amphoteric impurity in a boron-phosphide-based semiconductor, as well as in other Group III-V compound semiconductors (see xe2x80x9cHandotai Gijutsu (Jo)xe2x80x9d authored by Katsufusa Shohno, ninth printing, published by University of Tokyo Press on Jun. 25, 1992, p. 77). Regarding a boron phosphide semiconductor layer, a technique for formation of an n-type or p-type boron phosphide semiconductor layer which is not intentionally doped; i.e., an undoped boron phosphide semiconductor layer, by appropriately determining the vapor-phase growth temperature of the semiconductor layer (see the aforementioned xe2x80x9cHandotai Gijutsu (Jo),xe2x80x9d pp. 76-77) has been proposed. Boron vacancies and phosphorus vacancies are considered to determine the conduction type of an undoped boron phosphide semiconductor layer (see xe2x80x9c100 Semiconductor Techniques in the Super LSI Generation [III]xe2x80x9d authored by Katsufusa Shohno, appendix of a magazine xe2x80x9cElectronics,xe2x80x9d Vol. 27, No. 4, published by Ohmsha, Ltd. on Apr. 1, 1982, pp. 86-87).
Boron-phosphide-based semiconductor layers having different conduction types have been conventionally formed through doping with dopants of different types. When a pn-junction structure including a boron-phosphide-based semiconductor layer is produced, an intricate doping process employing different dopants is therefore required for formation of n-type and p-type boron-phosphide-based semiconductor layers. Even when an attempt is made to produce a light-emitting portion of pn-junction-type DH structure incorporating an undoped boron-phosphide-based semiconductor layer serving as a cladding layer to avoid the intricate doping process, diffusion of a Group IV element (i.e., dopant) from a light-emitting layer into the undoped boron-phosphide-based semiconductor cladding layer cannot be completely prevented. The intensity of light emitted from the light-emitting layer becomes inconsistent because of variation in the diffusion amount of the Group IV element, such as silicon, doped to a light emitting layer for enhancement of emission intensity, into an undoped boron-phosphide-based semiconductor layer. The resultant boron-phosphide-based semiconductor light-emitting device fails therefore to exhibit homogeneous emission intensity.
In the boron-phosphide-based semiconductor light-emitting device having a pn-junction-type DH structure including a light-emitting layer formed of a semiconductor layer doped with an appropriate amount of a Group IV element (i.e., a dopant for enhancing emission intensity), a boron-phosphide-based semiconductor light-emitting device exhibiting homogeneous and high emission intensity is advantageously produced provided that diffusion of the Group IV element into an undoped boron-phosphide-based semiconductor layer which is readily formed can be suppressed, thereby preventing reduction of the amount of the Group IV element contained in the light-emitting layer.
An object of the present invention is to provide a light-emitting portion of hetero junction structure which is employed for producing a boron-phosphide-based semiconductor light-emitting device exhibiting high emission intensity.
Accordingly, the above object of the present invention has been achieved by providing the following.
(1) A pn-junction-type boron-phosphide-based semiconductor light-emitting device comprising a single-crystal silicon (Si) substrate of first conduction type; a first boron-phosphide-based semiconductor layer of first conduction type formed of an undoped boron-phosphide-based semiconductor of first conduction type containing a Group IV element provided on the substrate; a light-emitting layer provided on the first boron-phosphide-based semiconductor layer, the light-emitting layer formed of a Group III-V semiconductor layer of first or second conduction type which is doped with an element belonging to Group IV of the periodic table provided on the first boron-phosphide-based semiconductor layer; and a second boron-phosphide-based semiconductor layer of second conduction type formed of a boron-phosphide-based semiconductor layer of second conductive type containing a Group IV element provided on the light-emitting layer, wherein the first boron-phosphide-based semiconductor layer, the light-emitting layer, and the second boron-phosphide-based semiconductor layer form a pn-junction hetero structure, and wherein said second conduction type is opposite said first conduction type.
(2) A pn-junction-type boron-phosphide-based semiconductor light-emitting device according to (1) above, wherein the first boron-phosphide-based semiconductor layer contains the same Group IV element as in the light-emitting layer.
(3) A pn-junction-type boron-phosphide-based semiconductor light-emitting device according to (1) or (2) above, wherein the first boron-phosphide-based semiconductor layer contains the Group IV element in an atomic concentration of 70% to 130% to that of the Group IV element contained in the light-emitting layer.
(4) A pn-junction-type boron-phosphide-based semiconductor light-emitting device according to any one of (1) through (3) above, wherein the Group IV element contained in the first boron-phosphide-based semiconductor layer and the light-emitting layer is silicon (Si).
(5) A pn-junction-type boron-phosphide-based semiconductor light-emitting device according to any one of (1) through (4) above, wherein the second boron-phosphide-based semiconductor layer is formed of an undoped boron-phosphide-based semiconductor layer of second conduction type.
(6) A pn-junction-type boron-phosphide-based semiconductor light-emitting device according to any one of (1) through (4) above, wherein the second boron-phosphide-based semiconductor layer is formed of a boron-phosphide-based semiconductor layer of second conduction type intentionally doped with a Group IV element.
(7) A pn-junction-type boron-phosphide-based semiconductor light-emitting device according to any one of (1) through (6) above, wherein the second boron-phosphide-based semiconductor layer contains the same Group IV element as the light-emitting layer.
(8) A pn-junction-type boron-phosphide-based semiconductor light-emitting device according to any one of (1) through (7) above, wherein the second boron-phosphide-based semiconductor layer contains the Group IV element in an atomic concentration of 70% to 130% to that of the Group IV element contained in the light-emitting layer.
(9) A pn-junction-type boron-phosphide-based semiconductor light-emitting device according to any one of (1) through (8) above, wherein the Group IV element contained in the second boron-phosphide-based semiconductor layer and the light-emitting layer is silicon (Si).
(10) A pn-junction-type boron-phosphide-based semiconductor light-emitting device according to (4) above, wherein the first boron-phosphide-based semiconductor layer contains silicon in an atomic concentration equal to or less than a concentration of phosphorus atoms occupying boron vacancies or a concentration of boron atoms occupying phosphorus vacancies.
(11) A pn-junction-type boron-phosphide-based semiconductor light-emitting device according to (9) above, wherein the second boron-phosphide-based semiconductor layer contains silicon in an atomic concentration equal to or less than a concentration of phosphorus atoms occupying boron vacancies or a concentration of boron atoms occupying phosphorus vacancies.
The present invention also provides the following.
(12) A method for producing a pn-junction-type boron-phosphide-based semiconductor light-emitting device as recited in any one of (1) through (11) above, which comprises forming a p-type boron-phosphide-based semiconductor layer at 1,000 to 1,200xc2x0 C. through an MOCVD method, and forming an n-type boron-phosphide-based semiconductor layer at 750 to 950xc2x0 C. through an MOCVD method.